1. Field of the Invention
This invention relates to an oil return function of an air conditioning system, including a compressor, an oil separator, a condenser, a expansion device, an evaporator, and accumulators connected to each other by piping, and the accumulator used with the refrigerant circuit and a method for manufacturing the accumulator.
2. Description of the Conventional Art
FIG. 41 shows a refrigerant circuit of a conventional air conditioning system, wherein numeral 1 is a compressor, numeral 2 is an oil separator, numeral 3 is a heat source machine heat exchanger serving as a condenser at the time, numeral 4 is a expansion device, numeral 5 is an indoor heat exchanger serving as an evaporator at the time, numeral 6 is a first accumulator, numeral 7 is a second accumulator, numeral 8 is a connection pipe for connecting the first and second accumulators 6 and 7, numeral 9 is a connection pipe for connecting the second accumulator 7 and the compressor 1, numeral 10 is an oil return bypass for connecting the oil separator 2 and the connection pipe 8, numeral 11 is an oil return device disposed at a midpoint in the pipe of the oil return bypass 10, numeral 12 is an oil return bypass for connecting the bottom of the first accumulator 6 and the connection pipe 8, numeral 13 is an oil return device disposed at a midpoint in the pipe of the oil return bypass 12, numeral 14 is a U effluent pipe of the second accumulator 7 connected to the connection pipe 9, numeral 15 is an oil return hole disposed at a midpoint in the U effluent pipe 14, and numeral 20 is a fluid pipe for connecting the heat source machine heat exchanger 3 and the expansion device 4.
Next, flows of a refrigerant and oil will be discussed. The high-temperature and high-pressure gas refrigerant discharged from the compressor 1 flows into the oil separator 2, which then separates oil therefrom. The gas refrigerant flows into the heat source machine heat exchanger 3, which exchanges heat between the gas refrigerant and air, water, etc., and condenses and liquefies the gas refrigerant. The liquid refrigerant flows through the fluid pipe 20 to the expansion device 4, through which the refrigerant becomes a low-pressure vapor-liquid two-phase condition and flows into the indoor heat exchanger 5, which then exchanges heat between the refrigerant and air, water, etc. As a result, the refrigerant becomes gas or a vapor-liquid two-phase condition at large dryness and returns via the first accumulator 6, connection pipe 8, second accumulator 7, and connection pipe 9 to the compressor 1. On the other hand, the oil separated by the oil separator 2 flows via the oil return device 11 and oil return bypass 10 to the connection pipe 8, then flows into the second accumulator 7. Since separation of the oil from the refrigerant at the oil separator 2 is not complete, oil together with the liquid refrigerant accumulates in the first accumulator 6. The oil and liquid refrigerant flow via the oil return device 13 and the oil return bypass 12 into the connection pipe 8, then flows into the second accumulator 7. The oil and liquid refrigerant accumulated in the second accumulator 7 flows through the oil return hole 15 to the U effluent pipe 14 and returns to the compressor 1.
Here, the oil and liquid refrigerant accumulated in the first accumulator 6 flows through the oil return bypass 12 to the connection pipe 8 because the total pressure difference of the dynamic pressure difference between the inside of the connection pipe 8 and the inside of the first accumulator 6, the differential pressure produced due to the friction loss of the gas refrigerant flowing through the connection pipe 8, and the liquid head produced according to the liquid level of the first accumulator 6 occurs across the oil return device 13. Likewise, the oil and liquid refrigerant accumulated in the second accumulator 7 flows to the U effluent pipe 14 because the total pressure difference of the dynamic pressure difference between the inside of the U effluent pipe 14 and the inside of the second accumulator 7, the differential pressure produced due to the friction loss of the gas refrigerant flowing through the U effluent pipe 14, and the liquid head produced according to the liquid level of the second accumulator 7 occurs across the oil return hole 15.
Generally, if an excess refrigerant is accumulated in the first accumulator 6 in large quantity, the oil separated by the oil separator 2 flows into the first accumulator 6 and is diluted with the liquid refrigerant in the first accumulator 6 and the oil return from the first accumulator 6 to the second accumulator 7 is delayed, causing oil exhaustion in the compressor 1. However, this does not occur even if an excess refrigerant is accumulated in the first accumulator 6 in large quantity, because the oil return bypass 10 is connected to the connection pipe 8. The oil separated by the oil separator 2 promptly returns via the second accumulator 7 to the compressor 1, providing a sufficient amount of oil in the compressor 1.
When the system is started in the condition in which the compressor 1 stops for a long time and a liquid refrigerant is allowed to stand in the shell of the compressor 1, the liquid refrigerant and oil in the shell are discharged in large quantity. The oil separator 2 traps the liquid refrigerant and oil, inhibiting efflux of a large amount of oil to the heat source machine heat exchanger 3, etc. Since the oil return bypass 10 is connected to the connection pipe 8, a large amount of the liquid refrigerant trapped in the oil separator 2 once flows into the second accumulator 7 without directly returning to the compressor 1 and returns through the oil return hole 15 to the compressor 1 little by little. Thus, damage to the compressor 1 caused by a rapid back flow of fluid can be inhibited. Generally, if an excess refrigerant is accumulated in the first accumulator 6 in large quantity, the oil together with the liquid refrigerant trapped in the oil separator 2 flows into the first accumulator 6 and is diluted with the liquid refrigerant in the first accumulator 6 and the oil return from the first accumulator 6 to the second accumulator 7 is delayed, causing oil exhaustion in the compressor 1. However, this can be suppressed even if an excess refrigerant is accumulated in the first accumulator 6 in large quantity, because the oil return bypass 10 is connected to the connection pipe 8.
Since the refrigerant circuit of the conventional air conditioning system is thus configured, the connection pipe 8 has large flow path resistance for causing the oil and liquid refrigerant accumulated in the first accumulator 6 to flow through the oil return device 13 into tile connection pipe 8, the U effluent pipe 14 has large flow path resistance for causing the oil and liquid refrigerant accumulated in the second accumulator 7 to flow through the oil return hole 15 into the U effluent pipe 14, and the pressure loss from the indoor heat exchanger 5 to tile compressor 1 is large and the refrigeration capability cannot sufficiently be exhibited because the liquid refrigerant passes through the first and second accumulators 6 and 7 in series.
The occupation space required for the first accumulator 6, the second accumulator 7, and the connection pipe 8 is large and a large number of points are brazed, reliability being lacked.
In addition, the conventional accumulator will be described as follows.
Next, FIGS. 42A and 42B show the structures of the conventional accumulators. The first accumulator 6 is a large pressure tank and the second accumulator 7 is a pressure vessel smaller than the first accumulator 6. The connection pipe 8 connecting the first and second accumulators 6 and 7 is a pipe thus bent because the oil return bypass 10 is connected to the upper side and the oil return bypass 12 to the lower side. Shown in the figure are the connection pipe 9 for connecting the second accumulator 7 and the compressor 1, the oil return bypass for connecting the bottom of the first accumulator 6 and the connection pipe 8, the oil return device disposed at a midpoint in the pipe of the oil return bypass 12, the U-effluent pipe of the second accumulator 7 connected to the connection pipe 9, and the oil return hole formed at a midpoint in the U-effluent pipe 14. Numeral 16 is an upper liquid level detector and numeral 17 is a lower liquid level detector. Since the conventional refrigerant circuit accumulators are thus configured, the liquid refrigerant passes through the first and second accumulators 6 and 7 in series. Therefore, the pressure loss from the evaporator 5 to the compressor 1 is large and the refrigeration capability cannot sufficiently be exhibited. The space occupied by the first accumulator 6, the second accumulator 7, and the connection pipe 8 is large, the long connection pipe 8 is required, and two pressure vessels are also required, thus the manufacturing costs are high. Further, a large number of points are brazed and reliability is lacked.